The present invention concerns a fire detector having a sensor group, which includes at least one fire detection sensors, and having a control and evaluation device, which is connected to the sensor group, set up to evaluate the signal supplied by the at least one fire detection sensor, and if necessary, set up to output at least one control signal for the fire detection sensor(s).
In a fire, the burning substances undergo a material and energetic conversion. In this case, soot particles, aerosols, and gases may form in addition to the ash remaining at the center of the fire. Based on the various physical processes in the air, such as thermal diffusion and turbulences, smoke particles are formed, which are detected by the fire detectors, optical smoke detectors, and ionization detectors used today.
The response characteristics of the optical smoke detectors and ionization detectors are a function of the type of fire, and may not be equally sensitive in all types of fires. In this context, the amount and the composition of the produced smoke play a role as influence variables (quantities). Thus, fires generating a small amount of smoke may not be detected as well as fires producing a large amount of smoke. In addition, the scattered-light smoke detector is dependent on the light being reflected from the smoke particles. This may result in the response characteristics of optical smoke detectors being nonuniform in various types of fires.
The energy released in the fire leads to an increase in temperature and an emission of radiation by the flames, which is detected by heat detectors (temperature detectors) and flame detectors.
While reliability of today""s fire detectors may be relatively high, single-sensor detectors may react to illusory quantities in certain situations. Due to the large number of fire detectors used, the number of false alarms attributable to them and the accompanying responses by the fire department may not be negligible. In certain application cases, conventional smoke detectors cannot be used, because either the ambient conditions are not suitable, or the fire intensity does not fall into the detection range of the detector.
Attempts may have been made in the industry to solve a part of this problem by combining certain technologies. In order to render the response characteristics of fire detectors more uniform, optical smoke detectors may be combined with an ionization detector or a temperature detector. In the planning and design of a fire detection system, the combination can mean providing various types of fire detector in one space. However, if various detection principles are already integrated in one fire detector, then a wide spectrum of possible fires can be detected by a single type of detector. An example of this is the combination of an optical smoke detector with a temperature sensor.
The gases formed during the burning of the combustible material are generally designated as combustion gases. In the starting phase of fires, CO, saturated and unsaturated hydrocarbons, alcohols, and acids are formed due to incomplete combustion. Organic materials burn as a rule, which is why CO, CO2, and H2O are the predominantly formed oxides. From approximately 200xc2x0 C. on, NOx is formed in the fire from the oxygen and nitrogen in the air.
To this day, it is believed that a detection system for the gases formed in a fire is yet to be used in fire detection technology. Reference is made here to a technical article of Appleby, D. Ellwood, S. H. : xe2x80x9cVolumetric fire detection using imaging of fire products and transport phenomenaxe2x80x9d, AUBE 1995.
An object of an exemplary embodiment for the present invention is to expand the operative range (range of application) of a fire detector equipped with conventional fire detection sensors, to design its response characteristics to be more uniform, to increase the reliability (signal-to-noise ratio) of the fire detector.
In this regard, the fire detector of an exemplary embodiment of the present invention is provided with a sensor group, which has at least one fire detection sensor; and is provided with a control and evaluation unit, which is connected to the sensor group, set up for evaluating the signal supplied by the at least one fire detection sensor, and if necessary, set up for outputting at least one control signal for the fire detection sensor(s), in which the sensory group also has a chemosensor or a chemosensor array, which is likewise connected to the control and evaluation unit for evaluating the detection signal of the chemosensor or chemosensor array, and which is set up on the basis of a chemical sensor-operation principle to detect gas and/or smoke emissions caused by a fire.
This fire detector according to an exemplary embodiment of the present invention, which can either be equipped with a single sensor that is a scattered-light sensor, ionization sensor, or a temperature sensor, or can alternatively combine two sensors as well, such as, for example, a scattered-light sensor and a temperature sensor, and may include an optoelectronic gas sensor functioning on an optode basis as a chemosensor, or an optoelectronic gas sensor array functioning on an optode basis as a chemosensor.
Since, in addition to the temperature increasing, gaseous combustion products are also formed in a fire, it is believed that these can improve the performance of fire detection, i.e. increase the signal-to-noise ratio and achieve a more rapid and more uniform fire-detection sensitivity, after being detected by the chemosensor or chemosensor array additionally provided in the exemplary embodiment of the present invention. Tests have shown that both accelerated response characteristics and an increased signal-to-noise ratio can be achieved by evaluating the additional signal(s) generated by a chemosensor or chemosensor array during a fire.
An optoelectronic gas sensor that functions on an optode basis using a chemical principle of sensor operation is the subject matter of German Patent No. 197 41 335, which is assigned to Robert Bosch GmbH. With such a chemosensor, miniaturized gas sensors, i.e. the so-called optodes, may be manufactured by using an optode sensor membrane to determine a physical and/or chemical parameter of a sample substance whose light-absorption properties change, based on an indicator substance contained in the sample substance, in response to at least indirect contact with a gas and/or gas mixture to be measured.
In this case, a chemosensor membrane may be made of a gas-sensitive polymer carrier material, to which an indicator substance from the following group of compounds is added:
azobenzenes, acetophenones, corrins, porphyrins, phthalocyanines, macrolides, porphyrinogens, nonactin, valinomycin, triphenylmethanes, diphenylmethanes, antracenes, antraquinones oxazoles, and/or complexes of these compounds with transition metals of the I-II and the IV-VIII subgroups.
German Published Patent Application No. 198 45 553, which is assigned to Robert Bosch GmbH, relates to producing an optoelectronic gas sensor array, which functions on an optode basis and is in the form of a chip, and in which several photosensitive elements separated from each other, and a light transmitter centrally located among them, are integrated in or on a semiconductor substrate. The photosensitive elements are each covered by segments of the optode material, and by a segment of a reference material; the optode material is made of a gas-sensitive polymer carrier material to which a chromium ionophore (ion carrier) is added, and the reference material is made of a polymer carrier material without a chromium ion carrier.
The fire detector of an exemplary embodiment of the present invention, which uses a chemosensor as an additional detector in the fire detector, allows the fire to be detected earlier because of the higher diffusion rate of the gases formed in a fire, and allows an increase in the signal-to-noise ratio through the evaluation of the combustion gases, since at least one additional quantity detected by the chemosensor and evaluated by the control and evaluation unit is added to the quantities detected by the conventional sensors.